The android duplicator was a mechanism discovered by Roger Korby on Exo III in or shortly after 2261. It was constructed centuries ago by the Old Ones, the race that once lived beneath the planet, and may be the pinnacle of their technical skill.

Starting with a blank and a living being, the mechanism could create a physically exact duplicate of that being, including synthetic organs whose autonomic rhythms matched those of the original. This process required that the naked original and blank be loaded onto a rotating platform. While this platform spun, the machine formed the blank into the android duplicate. At the conclusion of this process, the duplicate was only physically identical. One might expect such rapid rotation to be physically debilitating to the living being, but Kirk's experience in the machine revealed that this was not so. At the completion of this phase, he was physically unharmed.

A second stage, synaptic fusion, copied the target's thoughts and memories in the android. This stage also did not harm the original, but it was at least somewhat painful. Kirk was able to interfere with the outcome of this stage by keeping an atypical thought in the forefront of his mind. Subsequently, the android responded to a comment from Spock with this thought, apparently without realizing it was not something Kirk would normally say. Possibly, the android made this mistake because Korby stopped synaptic fusion when the android was, he believed, sufficient for his intended usage.

Roger Korby claimed that if synaptic fusion was carried to conclusion, the original being's consciousness could be transfered into the android duplicate. Such duplicates could then be programmed not to feel negative emotions or express negative traits. They formed the centerpiece of Korby's plan for a programmed utopia. Subsequent events revealed that the duplication process was not exact, and that the duplicates could, in fact, express traits other than those they were programmed to.

Control of the duplicator was accomplished from a complex control panel. The controls were color-coded but not otherwise labeled; presumably, one must have been well-trained in order to use the device successfully.

It was revealed that Korby, grievously injured, had constructed an android duplicate of himself, and had completely transferred his mind into it. Although the Korby android believed itself to be Korby, outsiders such as Kirk and Christine Chapel noted that its behavior was aberrant. Ultimately, Korby and all of the other androids were destroyed, leaving open the questions of when Korby actually died, and whether the Korby android was really Korby, or simply a machine convinced that it was Korby. (TOS: "What Are Little Girls Made Of?")